Original Date: 09/15/2003
Revision Date: 01/18/2007
Best Practice : Ball Lock Fixturing
Ball Lock fixturing has helped United Defense, L.P. Ground Systems Division Aiken reduce the average machine set-up time from 43 minutes per set-up to 16 minutes per set-up. Over time, this simple mounting system has allowed fixture changes to be reduced by approximately 300 percent.
United Defense, L.P. Ground Systems Division (UDLP GSD) Aiken operates as a business unit or commodity center within United Defense Corporation. The company is responsible for the machining, welding, and assembly of a variety of mechanical parts and assemblies for other United Defense divisions, facilities, and outside customers.
As a supplier of high mix/low quantity component parts, UDLP GSD Aiken constantly strives to implement Lean Manufacturing practices in all of its processes. In the high mix/low quantity environment, a company cannot set-up a machine once and leave it set-up to manufacture large quantities of parts. Instead, many set-ups must be performed over a short period of time, and each time it must be set-up to manufacture a low quantity of parts to be used or shipped within a short time period. The intent is to deliver to the customer what is needed, when it is needed, and in the quantity it is needed.
In order to minimize the non-value-added process of setting up machines for the manufacture of component parts, UDLP GSD Aiken is changing the manner in which vises and fixtures are located on the machine tables. Traditionally, the fixtures and vises were located on the machine tables using dowel pins or sine keys. The fixtures were then clamped to the machine tables using various clamping components such as threaded studs, tee nuts, bolts, or strap clamps.
Fixtures are now being located and clamped to the machine tables using ball lock shanks, normally four for each fixture. With the ball lock shank mounting process, a steel sub-plate is semi-permanently mounted to the machine using the existing tee slots and ways. The sub-plate is drilled and reamed to accept receiver bushings for the ball lock shanks and hold down bolts. The receiver bushing holes are located within the same hole pattern and spacing for all sub-plates. Aluminum fixture plates are then manufactured or purchased to mount the vises or holding fixtures. These plates contain the same hole pattern and spacing which match the sub-plates (Figure 2-1). Fixtures or vises are then mounted to the fixture plate using a variety of accessories, dowel pins, bolts, toe clamps, strap clamps, etc. When the machinist or operator wants to change a set-up for another job, the right fixture plate is obtained with the holding fixture or vise already mounted for the job; it is then mounted to the pre-drilled machine sub-plate. The mounting of the fixture plate is accomplished using two ball lock shanks and normally two hold down bolts. Figure 2-2 shows a ball lock fixture mounted on a machine table.
The use of ball lock fixturing provided UDLP GSD Aiken with many benefits including: Simplified set-ups with the reduction of clamping components needed in stock to attach fixtures to a machine table
Minimized set-up time (typically 15 to 30 minute set-up time has been reduced to three to five minutes)
Increased process capability through the repeatability of fixture location
Increased machine availability time
Eased set-up change-over
Reduced accident exposure
Reduced work instruction complexity
UDLP GSD Aiken’s use of ball lock fixturing and change-over procedures, along with other Lean Manufacturing practices, have reduced machine set-up and pre-set times from an average of 43 minutes per set-up to 16 minutes per set-up.
Figure 2-1. Ball Lock Sub-plate and Fixture Plate
Figure 2-2. Mounted Ball Lock Fixture
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